On 23 October 2017, which country signed the Paris Agreement on climate change, leaving the United States and Syria as the only two countries still outside the global climate pact at that time?

Introduction / Context:
The Paris Agreement is a global treaty aimed at addressing climate change by limiting global warming and promoting sustainable development. Almost every country in the world has joined it. However, in the early years after its adoption, a few countries had not yet signed or ratified the agreement. This question asks which specific country signed the Paris Agreement on 23 October 2017, an event that left only the United States and Syria outside the pact at that time, a commonly referenced fact in international affairs questions.

Given Data / Assumptions:

• The date is 23 October 2017.
• The action is signing or joining the Paris Agreement on climate change.
• After this, only the United States and Syria were still outside the agreement.
• We must choose the correct country from a list of four options.

Concept / Approach:
Initially, Nicaragua did not join the Paris Agreement, not because it opposed climate action, but because its leaders felt the agreement was not strong enough. Later, Nicaragua decided to join the global consensus and formally signed the treaty on 23 October 2017. After this step, only the United States (which had announced its intention to withdraw) and war-torn Syria remained outside. To answer correctly, we must recall which of the listed countries changed its position in October 2017 and joined the agreement on that specific date.

Step-by-Step Solution:

Verification / Alternative check:
International news and official treaty status updates from 2017 state clearly that Nicaragua formally joined the Paris Agreement on 23 October 2017. At that point, commentators pointed out that only the United States and Syria remained outside the accord. Colombia, Peru, and Uganda were early signatories or ratifying parties and thus do not match the timeline described in the question. This consistency between news records and the question's wording confirms that Nicaragua is the correct option to choose.

Why Other Options Are Wrong:
Colombia had already signed and ratified the Paris Agreement well before October 2017 and is not linked with that date in the context of joining. Peru is also a party to the agreement and was not one of the holdouts. Uganda likewise participated in the agreement earlier and was not highlighted as a last-minute joiner in 2017. Therefore, none of these three countries fit the description of signing the agreement on 23 October 2017 and leaving only the United States and Syria outside.

Common Pitfalls:
Students may confuse Nicaragua with other Latin American countries or simply guess without recalling the specific news. Another pitfall is to assume that any developing country in the options could be the answer, without checking the exact date. To avoid such mistakes, remember the story that Nicaragua initially criticized the Paris Agreement as not ambitious enough but later decided to join, and that this event was reported as making the treaty almost universal. Linking Nicaragua with this narrative helps you choose accurately in exam settings.

Final Answer:
On 23 October 2017, the country that signed the Paris Agreement was Nicaragua.